This handsome campo mimosa, which was perceived by Per Dusén to be allied to but (in herbarium notation) different from M. regnellii, was mistaken by Burkart for that species. It differs from var. regnellii in virgate habit, with few large leaves below mid-stem and an extremely long efoliate and multicapitulate pseudoraceme, branched or not, overtopping the foliage by 5-8 dm, and further by concolorous, symmetrically linear-oblong leaflets with a centric costa either solitary or accompanied on each side by a narrowly intramarginal nerve. In the asymmetrically costate leaflets of M. regnellii the midrib is accompanied on the posterior side alone by primary nerves and the margin of the leaflets is rimmed with pallid tissue. The habit of M. regnellii, when all varieties are considered, is somewhat diverse, but the mature plants are usually distinctly fruticose, with defoliate trunks and densely leafy homotinous branches. The varieties of M. regnellii sympatric or nearly so with M. deceptrix in eastern Paraná differ further in short leaves and few pinnae.